1. Field of Invention
The invention relates an angular rate sensing device for an angular rate sensor or a micro gyroscope and, in particular, to an angular rate sensing device having a plurality of proof masses employed as a resonant structure for increasing the signal-sensing areas, such that greater Coriolis force is generated and Coriolis force intensity increases. Furthermore, the sensing areas and the intensity of the sensing signals are increased.
2. Related Art
The gyroscope is a device that measures rotating angles or angular rates by using the inertia principle. One of these is a micro gyroscope manufactured by micro technology. It has been used widely in many fields, such as anti-overturning systems for cars, airbag systems, industrial robots, 3D mice, and Global Positioning Systems. The characteristics of small volume, light weight, and low cost have made micro gyroscopes, which are becoming potentially commercial sensors, penetrate the market of traditional gyroscopes
Due to the constraints of Microelectromechanical manufacturing technology and the consideration of endurance, most gyroscopes are vibratory. Besides the noise signal ratio of the signal sensing circuits, the structure is another element that affects the sensitivity and the performance. In the related art, the most important element, which also affects the performance of the micro gyroscope, is the ring-like vibrator. Patents relating to these technology fields are U.S. Pat. Nos. 5,450,751, 5,872,313, 5,889,207, 6,282,958, 6,305,222, and 6,481,285.
Patent '751 discloses a microstructure for a vibratory gyroscope. The microstructure has a ring portion supported in such a fashion as to allow substantially undamped, high-Q radial vibration. The ring portion is electrically conductive and comprises a charge plate for a plurality of radially disposed charge conductive sites around its perimeter for sensing radial displacements thereof. The ring, its support and charge conductive sites are formed within sacrificial molds on one surface of a conventional silicon substrate, which may comprise a monolithic integrated circuit.
Patent '313 discloses a motion sensor having a micromachine sensing element and electrodes formed on a silicon chip. The sensing element includes a ring supported above a substrate so as to have an axis of rotation normal to the substrate. Surrounding the ring is at least one pair of diametrically-opposed electrode structures. The sensing ring and electrode structures are configured to include interdigitized members whose placement relative to one another enables at least partial cancellation of the differential thermal expansion effect of the ring and electrodes.
Patent '207 discloses a rate of rotation sensor structured as a micromechanical component on the surface of a substrate. The rate of rotation sensor has a ring with drive elements and detection elements. The ring is made to oscillate by means of the drive elements, and the deformation of the ring that results from Coriolis forces is detected by the detection elements.
Patent '958 discloses an angular rate sensor including a ring-like resonator mounted by support beams extending from the inner periphery of the ring to a boss on a base. The support beams are flexible and allow the resonator to vibrate in response to an electrostatic drive in a substantially undamped oscillation mode to permit the resonator to move relative to the support in response to turning rate. Electrostatic sensors are provided for sensing movement of the resonator.
Patent '222 discloses a motion sensor including a micromachined sensing structure and a number of capacitive electrodes disposed about the periphery thereof. The sensing structure includes a ring supported above a substrate, and a number of springs attached to a post positioned at the center of the ring. Certain diametrically opposed capacitive electrodes are configured as drive electrodes, and other diametrically opposed capacitive electrodes, positioned 90 degrees relative to the corresponding drive electrodes, are configured as sense electrodes.
Patent '285 discloses a micro-machined angle measurement gyroscope including a substrate; a proof mass coupled to the substrate by an isotropic suspension; a plurality of drive electrodes configured to cause the proof mass to oscillate; and a plurality of sense electrodes configured to sense the motion of the proof mass in the plane of the substrate.
However, the aforementioned related art has some technical problems that need to be solved. For example, the mass of the resonant structure is so small that the intensity of Coriolis force is not significant. The supporting structure is not symmetrical so that the resultant Coriolis force does not indicate the original node, which may cause measurement error. Also, the signal-sensing area is not large enough so that the intensity of the signals is small, and therefore the difficulty of measurement increases. Although the high aspect ratio manufacture technology may reform these problems, the expense and machine investment may be prohibitive. Therefore, there is an urgent need for developing a new micro angular rate-sensing device.